1. Technical Field
The present invention relates generally to power tools such as rotatable drills, power screwdrivers, and rotatable cutting devices. More particularly, the present invention relates to a transmission for a multi-speed transmission for a rotary power tool.
2. Discussion
Modernly, manufacturers of power tools have introduced rotary power tools that have variable speed motors in an attempt to permit the users of these tools with sufficient control over the output speed of the tool so as to permit them to perform diverse operations without resort to additional, specialized tools. Many of the tools that are commercially available include a three-stage, two-speed transmission that permits even greater control over speeds of these tools.
Typically, the known transmission arrangements have lacked a transmission arrangement that could produce a wide range of output speeds and torques that would permit the tool to perform diverse operations such as drilling holes with a large diameter hole saw, installing drywall screws or large diameter lag screws, and performing high-speed drilling operations. The single or dual speed transmissions that were generally employed in these tools typically did not have sufficient speed reducing capacity to permit these transmissions to be diversely employed as configuring these tools for high torque operations tended to impair their high speed performance. Furthermore, the rechargeable batteries that were employed in many of the early cordless rotary power tools were not well suited for use in low-speed, high torque operations due to the amount of energy that is consumed and the rate with which the energy is consumed by the power tool during such operations. Consequently, consumers were often forced to purchase two different rotary power tools, a medium-duty tool for xe2x80x9cstandardxe2x80x9d applications such as drilling and fastening, and a heavy-duty tool having a low-speed, high torque output for more demanding tasks.
With the advent of the modern high capacity, high voltage battery, it is now possible to meet the energy demands of a power tool that is used in low-speed, high torque operations. There remains, however, a need in the art for a power tool transmission having a relatively large range in its speed reducing capacity.
In one preferred form, the present invention provides a drive train for a power tool. The drive train includes a housing, a transmission and a speed selector mechanism. The transmission has first, second and third reduction gear sets, with two of the reduction gear sets being configured to operate in an active mode for performing a speed reduction and torque multiplication operation and an inactive mode. The speed selector mechanism has a switch portion that is coupled to the housing for movement between first, second and third positions and an actuator portion that is coupled to the transmission. The actuator portion is configured to move two of the reduction gear sets between the active and inactive modes in response to movement of the switch portion between the first, second and third positions.
In another preferred form, the present invention provides a transmission assembly for transmitting torque to an output shaft in a power tool. The transmission assembly includes a housing, a first transmission portion and a second transmission portion. The housing includes a wall member that defines a transmission bore. The first transmission portion has a first input member, a first output member and a first reduction element. The first input member is configured to receive a first intermediate output torque and the first output member configured to output a second intermediate output torque. The first reduction element operable in a first condition wherein the first transmission portion multiplies the first intermediate output torque by a predetermined first amount. The first reduction element further operable in a second condition wherein the first transmission portion multiplies the first intermediate output torque by a predetermined second amount. The second transmission portion includes a second input member, a second output member and a second reduction element. The second input member is configured to receive the second intermediate output torque and the second output member configured to output an output torque to the output shaft. The second reduction element operable in a first condition wherein the second transmission portion multiplies the second intermediate output torque by a predetermined third amount. The second reduction element further operable in a second condition wherein the second transmission portion multiplies the second intermediate output torque by a predetermined fourth amount.
In yet another preferred form, the present invention provides a power tool having a motor and a transmission. The motor has an output shaft and produces an input torque. The transmission assembly has a housing having a wall member that defines a transmission bore and a transmission having first, second and third planetary gear sets. The first planetary gear set has a first ring gear, a first sun gear and a first planet gear assembly. The first planet gear assembly has a first planet carrier and a plurality of first planet gears. The first planet carrier rotatably coupled to the first sun gear. The first planet carrier has a plurality of pinions for rotatably supporting the plurality of first planet gears. The first sun gear is configured to receive the input torque. The first planet carrier includes a second sun gear and being configured to transmit the first intermediate output torque to the second planetary gear set. The plurality of first planet gears meshingly engaged with the second sun gear and the first ring gear. The first ring gear axially positionable in a first condition wherein the first ring gear is fixed relative to the housing.
The second planetary gear set includes a second ring gear and a second planet gear assembly. The second planet gear assembly has a second planet carrier and a plurality of second planet gears. The second planet carrier has an output sun gear and a plurality of pinions for rotatably supporting the plurality of second planet gears. The second sun gear is meshingly engaged with the plurality of second plane gears and transmits the first intermediate output torque thereto. The output sun gear configured to output a second intermediate output torque. The plurality of second planet gears are also meshingly engaged with the second ring gear. The second ring gear is axially positionable in a first condition wherein the second ring gear is fixed relative to the housing to prevent relative rotation therebetween. The second ring gear is also axially positionable in a second condition wherein the second ring gear is rotatable within the transmission bore.
The third planetary gear set includes a third ring gear and a third planet gear assembly. The third planet gear assembly has a third planet carrier and a plurality of third planet gears. The third planet carrier has an output member and a plurality of pinions that rotatably support the plurality of third planet gears. The plurality of third planet gears are meshingly engaged with the third ring gear and the output sun gear and are configured to receive the second intermediate output torque. The output member is configured to output an output torque. The third ring gear is axially positionable in a first condition wherein the third ring gear is fixed relative to the housing to prevent relative rotation therebetween. The third ring gear is also axially positionable in a second condition wherein the third ring gear is rotatable within the transmission bore.